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Old 17th December 2012, 11:43 PM   #8131
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Quote:
Originally Posted by Joachim Gerhard View Post
I found it, post 42, that was a long time ago. I did also a balanced version of that one.
Post 42 has a little DC offset at the input that is the difference of the PNP and NPN Ube.
Could be solved by swapping the Ube transdiodes from one gender to the other.
The we have a PN NP drop on both polarities. Shunting the transdiodes with high value elcaps will lower the noise by 3dB.
Yes, the link shows post 42.

The small offset is no problem if you adjust for instance one of the input current sources.

Some improvements to this basic circuit are possible in order to arrive at what is my preferred topology.
I am curious how you derived this "Malcolm Hawksford Homage", I am not familiar with the abbreviation LFD.

Quote:
Originally Posted by Joachim Gerhard View Post
It has an interesting gain structure : I-U, U-I, I-U. U-I
I don't agree with that, it is current in, current out and buffer.

Last edited by as_audio; 17th December 2012 at 11:47 PM.
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Old 17th December 2012, 11:50 PM   #8132
MiiB is offline MiiB  Denmark
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Think the buffer is too complex and fast....

The current "circle" driving the circuie is very suitable for a nice servo soulution
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Old 17th December 2012, 11:50 PM   #8133
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Ube is a very weak function of idle so that does not work. There are other ways. Anyway.
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Old 18th December 2012, 12:00 AM   #8134
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Quote:
Originally Posted by MiiB View Post
Think the buffer is too complex and fast....
The buffer as shown in post 42 is straightforward and standard in integrated circuits.
It can be built easily with discrete transistors also. The values shown are not significant
(editor presets). But you can obviously use a simple buffer also.
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Old 18th December 2012, 12:02 AM   #8135
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Quote:
Originally Posted by Joachim Gerhard View Post
Ube is a very weak function of idle so that does not work. There are other ways. Anyway.
I was intrigued by your offset warnings earlier, so I did it this way with success.
Sure, Vbe is a weak function of Ic, but Vbe difference is not ..
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Old 18th December 2012, 12:04 AM   #8136
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OK, adjusting both sides.
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Old 18th December 2012, 12:05 AM   #8137
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One side is enough of course
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Old 18th December 2012, 12:09 AM   #8138
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Quote:
Originally Posted by Joachim Gerhard View Post
OK, adjusting both sides.
Once upon a time the founder of a famous german high-end manufacturer told me to adjust both sides,
one side for offset and the other for total idle.
I looked at him but díd not answer.
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Old 18th December 2012, 01:02 AM   #8139
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C:
On my Nobrainer thread there are more varieties of bipolar, transimpedance inputs with offset adjust. Sure, no problem, can be solved.
I think it is overrated but some here even do not accept a tiny amount of DC through the cartridge. We have beaten that red herring so many times to death that it started to smell funny.
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Old 18th December 2012, 01:06 AM   #8140
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MPP thread, post 2, right at the beginning shows the balanced variant.
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